Field: The invention is in the field of gas or liquid fueled space heating furnaces which draw combustion air from the inside of the buildings which they heat or from a separate fresh air supply connected to an external source and exhaust the combustion gases exteriorly of the buildings.
State of the Art: Furnaces fueled by various kinds of gases such as natural gas, methane, propane, etc., or liquids, such as fuel oil, are customarily used for space heating of buildings and other enclosures of various kinds. Hot air furnaces fueled by natural gas are widely used for heating the interior of homes. Such space heating furnaces have been constructed in many different ways, but in all cases, they require a fresh air supply, wherein the fresh air is either drawn from the interior of the building or, in some special cases, from a separate connection which conducts the fresh air directly from the exterior of the building into the furnace area. Combustion gases are exhausted from the combustion chamber to a flue which conducts the gas by way of a stack or chimney to the atmosphere exteriorly of the building. To provide proper draft in the flue, air from the fresh air supply is drawn into the flue through a diverter air opening therein.
A significant waste of energy results during periods when the furnace is not operating, i.e., when fuel is not being burned in the furnace, as a result of:
A. Heat loss due to warm air escaping to the exterior of the building through the air inlet to the combustion chamber and the air drawn into the flue through the diverter air opening in the flue.
B. Unnecessary cooling of the furnace heat exchanger which is caused by heat transfer from the previously heated surfaces of the heat exchanger to the air being exhausted to the exterior of the building via the flue.
To alleviate these heat losses, it has been suggested that dampers be installed in the exhaust flues of such furnaces, and it is a common expedient to utilize such dampers in coal-burning furnaces and fireplaces. However, similar dampers in modern automatically controlled gas and liquid fueled furnaces have been considered to be highly dangerous. An extreme hazard exists if the burner of the furnace to which such a damper is attached comes on without the damper opening the vent or flue.
Objective: The objective of this invention was to develop a reliable, safe mechanism by which gas flow through the draft system of the furnace is automatically closed when the burner is not operating and opened when it is operating.